Relationship between morphology, crystallization behavior and mechanical properties of polypropylene micro- and nanocomposites

Polypropylene (PP) micro- and nano-composites were studied theoretically and experimentally in detail. Several important fundamental issues were addressed. Morphology studies found that there was a thin interface layer between PP matrix and calcium carbonate (CaCO3) nanoparticles. Both transition electronic microscopy (TEM) and scanning electronic microscopy (SEM) observations revealed that the bonding between the CaCO3 particles and interfacial layer was weak. The crystallization behavior of the PP/CaCO3 nanocomposites was fully investigated by differential scanning calorimetry (DSC) and optical microscopy (OM). The studies on the isothermal crystallization behaviors of PP nanocomposites revealed that, compared with pure PP and PP/CaCO3 microcomposites, the addition of nanoparticles in PP matrix induced stronger heterogeneous nucleation, and therefore increased the crystallization rate. An optimum concentration of nano-CaCO3, 10 wt%, with the highest crystallization rate in PP/CaCO3 nanocomposites was achieved. The incorporation of the nano-CaCO3 particles in the PP matrix increased the Young's modulus but decreased the yield stress of the composites. The nanoparticle debonding and cavitation inducing massive shear deformation of PP matrix between particles were identified as the major microdeformation mechanisms of PP/CaCO3 nanocomposites under uniaxial loading. The relationships between the yielding behavior and morphological characteristics of nanocomposites were analyzed by the Eyring equation. Furthermore, the activation volume and activation energy were analyzed based on the morphologies of these nanocomposites. Comparison between PP/CaCO3 and PP/talc composites revealed that the interfacial adhesion play a crucial role in determining their morphology, and further influenced the crystallization behavior, and mechanical and physical properties